Just updated from fedora 18 to 19 -- mostly trouble-free and very impressive.
One issue: when I boot up this is what happens:
1) grub does its thing; I let it time out to the default; OK.
2) plymouth starts: the little expanding white teardrop thingy that will turn into the "f" logo; OK.
3) About 15% percent into the expansion (a second or two), video output quits altogether. Black screen, and my monitor posts its "No video input" message.
The first time this happened I thought the system was screwed, but actually if I wait 10 seconds or so, video comes back with the login screen.
This is on a Dell XPS box with Radeon HD 6450 video. No such problem with fedora 18.